Dehydrogenating a less costly C2 to C12 chain alkyl compound (for example, ethane, butene, isobutane, ethyl benzene, ethyl cyclohexane, etc., also simply referred to as chain alkyl compound hereinafter) to the corresponding chain alkenyl compound, which is more valuable, has drawn more and more attention of the industry and the academia. For example, as a very important starting material for the organic chemical industry, isobutene among the C4 olefins traditionally mainly originates from an apparatus for producing ethylene by a naphtha stream cracking process or an apparatus by heavy oil fluid catalytic cracking in a processing plant. As the modern chemical industry is growing demand for isobutene as a starting material, a process for producing isobutene from isobutane by a dehydrogenation process has been developed and has ranked the third as a source of isobutene in the world.
The prior art isobutane dehydrogenation process in an industry scale is generally conducted under an oxygen free condition, by using a Cr based catalyst or a Pt based catalyst. For example, the Catofin process of the ABB Lummus company, the Oleflex process of the UOP company, the Star process of the Philips company, the Linde process of the Linde company and the FBD-4 process of the Snamprogetti company can be exemplified.
These prior art processes suffer from such problems as, use of a Cr based catalyst which is toxic, or a Pt based catalyst which is expensive, which lead to cost or environment pollution concerns. Further, restricted by the thermodynamic equilibrium of the dehydrogenation reaction, these prior art processes give a relatively lower isobutane conversion level. It may be possible to increase this conversion by elevating the reaction temperature, however, a relatively high reaction temperature will generally lead to sintering, coke deposition and deactivation of the catalyst. For this reason, there still remains room for the prior art catalyst to improve its high temperature resistance.
The dehydrogenation under a CO2 atmosphere has drawn more and more attention. Ogonowski et al compared the dehydrogenation activity for isobutane over a V—Mg—O catalyst having a surface area of 21 m2 g−1 under a reaction temperature of 600° C., under an inert atmosphere (He), with that under a CO2 atmosphere. The result reveals that the catalyst exhibits an improved dehydrogenation activity under the CO2 atmosphere, resulting in an isobutane conversion as high as 13% and an isobutene selectivity of more than 80% (Catalysis Communications, Vol. 11, 2009, pp. 132-136). Shimada et al found that the isobutane conversion can reach at as high as 23% under 600° C. by using an activated carbon supported Fe2O3 catalyst, with an isobutene selectivity of 80%. Unfortunately, the activity of the catalyst decays very rapidly, reflected by an isobutane conversion reduced to 13% after 3 hours (Applied Catalysis A: General, Vol. 168, 1998, pp. 243-250). Ding et al found that both an activated carbon supported Cr2O3 catalyst and an activated carbon supported NiO catalyst exhibit a relatively high initial activity for isobutane dehydrogenation in a CO2 atmosphere, while both suffer from a relatively rapid activity decay (Chinese Chemical Letters, Vol. 19, 2008, pp. 1059-1062; Journal of Molecular Catalysis A: Chemical, Vol. 315, 2010, pp. 221-225).
Nevertheless, these prior art catalysts are incapable of concretely meet with some requirements in practice due to their insufficient isobutane conversion and isobutene selectivity, and there still remains room for further improvement in this regard. Further, the rapid activity decay is also a hard problem to be solved.
The prior art catalysts suffer from the similar defects when used for dehydrogenating other C2 to C12 chain alkyl compounds than isobutane.
Under this circumstance, there still need a catalyst in this field, especially a catalyst for dehydrogenating a C2 to C12 chain alkyl compound, which is cheap in cost, friendly to the environment, and satisfactory in high temperature resistance to sintering, with a highly improved and a relatively stable catalytic activity, and capable of solving the problems associated with the prior art catalysts.